1. Field of the Invention
This invention relates to a method and an apparatus for bending and tempering glass sheets, and more particularly concerns bending flat glass sheets into curved glass sheets adapted for use in automobiles as sidelites (side windows) and backlites (back windows) or for use in buildings, by positioning longitudinal rows of disc rollers or mini-rollers to form transverse curved contours which receive a hot flat glass sheet and form it into a desired contour. The longitudinal rows of rollers may be raised and lowered to different controlled vertical elevations to produce glass sheets that are bent into transverse curves as viewed from the unloading end of the machine.
2. Description of the Prior Art
Many techniques for bending glass sheets are known. A simple technique is to support the edge portions of the glass sheet on the edge portions of a horizontally positioned contoured perimeter mold having a depressed center portion, and heat the glass sheet to cause its unsupported center portion to sag by gravity to conform to the shape of the depressed center portion of the mold. This gravity process is slow. It can be speeded-up by pressing the hot glass sheet between a pair of upper and lower contoured molds instead of depending on gravity to bend it, as disclosed by Seymour in U.S. Pat. No. 3,846,104.
U.S. Pat. No. 3,476,540 to Ritter et al. discloses a glass bending arrangement having a single vertically-rising lower bending mold on which the hot glass is bent by gravity. Disadvantageously, the bent glass sheets must pass without edge support along a roller conveyor into a tempering zone.
U.S. Pat. No. 3,600,150 to Rougeux shows a glass bending arrangement where the heat softened glass sheet is slipped from a roller conveyor onto a flexible hammock and thereafter press-bent between upper and lower forming molds. The purpose of the flexible hammock is to support the glass sheet initially out of contact with the rigid shaping mold surfaces. A major reconstruction of the apparatus is required when a change in the glass shape is desired.
U.S. Pat. No. 4,300,935 to Seymour discloses a glass bending arrangement wherein a heat softened glass sheet is elevated by a flat vacuum platen that raises the glass sheet and drops it onto a bending mold to bend it by gravity. After bending the glass, the bending mold carrying the bent glass is passed into a tempering station by a shuttle where the bent glass sheet is tempered.
It has long been desired to provide a method and apparatus for bending large sheets of glass, especially for bending the larger bent lites of glass specified by architects for buildings. The major problem with existing horizontal mold bending equipment is that most use horizontally positioned perimeter molds, which leave unsupported a large area of glass in the center of the glass sheet. The unsupported area of glass may be the subject of uncontrolled sagging when the glass is at the softening point for bending.
Another problem with conventional glass bending machines is their lack of versatility and the high cost of changeovers from one size glass sheet to another. Conventional bending machines do not have the ability to run a small number of a shaped glass sheet of one size and then quickly change to glass sheets of a different shape and size without the loss of valuable production time.